IMAP APPEND fails when inMemorySizeLimit is exceeded

When the APPENDed message exceeds the memory size limit, ImapRequestFrameDecoder allocates a file scoped to command decoding and not command execution.

We need to review the lifecycle of this file in order to dispose it only after the command being executed.

My idea would be to register closeables to the channel and dispose them once the message is processed.

Such a move will allow using files instead of memory for large mails, reducing the memory footprint of large APPEND.

Note that server/protocols/imap is not tested so as part of this ticket, as we need to write a faulty test, we also need to write such tests.